Android登錄：應用程序崩潰時條目無效？

Question

我正在使用JSON和MYSQL登錄應用程序它工作正常，如果我輸入用戶名和密碼的正確值，但每當我輸入一個無效的輸入它崩潰？

另一個奇怪的部分是，每當我登錄然後註銷，然後嘗試一個無效的條目，它使成功登錄。它就像它保存了以前的值，並且從不重置？

logcat的報告

09-22 18:52:26.838: E/AndroidRuntime(1924): FATAL EXCEPTION: main 
09-22 18:52:26.838: E/AndroidRuntime(1924): Process: com.learn2crack.tab, PID: 1924 
09-22 18:52:26.838: E/AndroidRuntime(1924): java.lang.NullPointerException 
09-22 18:52:26.838: E/AndroidRuntime(1924):  at com.learn2crack.tab.Login$ProcessLogin.onPostExecute(Login.java:202) 
09-22 18:52:26.838: E/AndroidRuntime(1924):  at com.learn2crack.tab.Login$ProcessLogin.onPostExecute(Login.java:1) 
09-22 18:52:26.838: E/AndroidRuntime(1924):  at android.os.AsyncTask.finish(AsyncTask.java:632) 
09-22 18:52:26.838: E/AndroidRuntime(1924):  at android.os.AsyncTask.access$600(AsyncTask.java:177) 
09-22 18:52:26.838: E/AndroidRuntime(1924):  at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:645) 
09-22 18:52:26.838: E/AndroidRuntime(1924):  at android.os.Handler.dispatchMessage(Handler.java:102) 
09-22 18:52:26.838: E/AndroidRuntime(1924):  at android.os.Looper.loop(Looper.java:136) 
09-22 18:52:26.838: E/AndroidRuntime(1924):  at android.app.ActivityThread.main(ActivityThread.java:5017) 
09-22 18:52:26.838: E/AndroidRuntime(1924):  at java.lang.reflect.Method.invokeNative(Native Method) 
09-22 18:52:26.838: E/AndroidRuntime(1924):  at java.lang.reflect.Method.invoke(Method.java:515) 
09-22 18:52:26.838: E/AndroidRuntime(1924):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779) 
09-22 18:52:26.838: E/AndroidRuntime(1924):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595) 
09-22 18:52:26.838: E/AndroidRuntime(1924):  at dalvik.system.NativeStart.main(Native Method) 

互聯網連接後onclick事件的代碼片段檢查 login.java

/** 
    * Async Task to get and send data to My Sql database through JSON respone. 
    **/ 
    private class ProcessLogin extends AsyncTask<String, String, JSONObject> { 

    private ProgressDialog pDialog; 

    String username,password; 

    @Override 
    protected void onPreExecute() { 
     super.onPreExecute(); 

     inputusername = (EditText) findViewById(R.id.username); 
     inputPassword = (EditText) findViewById(R.id.pword); 
     username = inputusername.getText().toString(); 
     password = inputPassword.getText().toString(); 
     pDialog = new ProgressDialog(Login.this); 
     pDialog.setTitle("Contacting Servers"); 
     pDialog.setMessage("Logging in ..."); 
     pDialog.setIndeterminate(false); 
     pDialog.setCancelable(true); 
     pDialog.show(); 
    } 

    @Override 
    protected JSONObject doInBackground(String... args) { 

     UserFunctions userFunction = new UserFunctions(); 
     JSONObject json = userFunction.loginUser(username, password); 
     return json; 
    } 

    @Override 
    protected void onPostExecute(JSONObject json) { 
     try { 
      if (json.getString(KEY_SUCCESS) != null) { 

       String res = json.getString(KEY_SUCCESS); 

       if(Integer.parseInt(res) == 1){ 
        pDialog.setMessage("Loading User Space"); 
        pDialog.setTitle("Getting Data"); 

        Intent upanel = new Intent(getApplicationContext(), MainActivity.class); 
        upanel.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP); 
        pDialog.dismiss(); 
        startActivity(upanel); 
        /** 
        * Close Login Screen 
        **/ 
        finish(); 
       }else{ 

        pDialog.dismiss(); 
        loginErrorMsg.setText("Incorrect username/password"); 
       } 
      } 
     } catch (JSONException e) { 
      e.printStackTrace(); 
     } 
    } 
} 
public void NetAsync(View view){ 
    new NetCheck().execute(); 
} 

}

從userfunctions.java登錄方法

public JSONObject loginUser(String email, String password){ 
     // Building Parameters 
     List<NameValuePair> params = new ArrayList<NameValuePair>(); 
     params.add(new BasicNameValuePair("tag", login_tag)); 
     params.add(new BasicNameValuePair("email", email)); 
     params.add(new BasicNameValuePair("password", password)); 
     JSONObject json = jsonParser.getJSONFromUrl(loginURL, params); 
     return json; 

Answer 1

1.定義在LoginActivity像另一個靜態字符串變量：

private static String KEY_ERROR = "error"; 

2.Modify你對你的onPostExecute()方式類似：

@Override 
     protected void onPostExecute(JSONObject json) { 
      try { 
       if (json.getString(KEY_SUCCESS) != null) { 

        String res = json.getString(KEY_SUCCESS); 
        String red = json.getString(KEY_ERROR); 

        if (Integer.parseInt(res) == 1) { 

         pDialog.setMessage("Dashboard"); 
         pDialog.setTitle("Loading."); 

         Intent upanel = new Intent(getApplicationContext(), 
           MainActivity.class); 
         upanel.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP); 
         pDialog.dismiss(); 
         startActivity(upanel); 
         /** 
         * Close Login Screen 
         **/ 
         finish(); 

        } else if (Integer.parseInt(red) == 1) { 

         pDialog.dismiss(); 
         Toast.makeText(getApplicationContext(), "Wrong Email/Pw", 
         Toast.LENGTH_SHORT).show(); 
        } 
       } 
      } catch (JSONException e) { 
       e.printStackTrace(); 
      } 
     } 

3.修改你的web服務（假設你使用PHP）：

的index.php

// check for tag type 
    if ($tag == 'login') { 

     // Get data 
     $email = $_POST['email']; 
     $password = $_POST['password']; 

     // check for user 
     $user = $db->getUserByEmailAndPassword($email, $password); 

     if ($user != false) { 

      // user found 
      // echo json with success = 1 
      $response["success"] = 1; 
      $response["error_msg"] = "Correct credentials!"; 
      echo json_encode($response); 

     } else { 

      // user not found 
      // echo json with error = 1 
      $response["error"]  = 1; 
      $response["error_msg"] = "Incorrect email or password!"; 
      echo json_encode($response); 
     } 
    } 

DB_Functions.php

/** 
    * Verifies user by email and password 
    */ 

    public function getUserByEmailAndPassword($email, $password) { 
     $result = mysql_query("SELECT * FROM users WHERE email = '$email'") or die(mysql_error()); 
     // check for result 
     $no_of_rows = mysql_num_rows($result); 
     if ($no_of_rows > 0) { 
      $result = mysql_fetch_array($result); 
      $salt = $result['salt']; 
      $encrypted_password = $result['encrypted_password']; 
      $hash = $this->checkhashSSHA($salt, $password); 
      // check for password equality 
      if ($encrypted_password == $hash) { 
       //Update last login of user 
       //mysql_query("UPDATE users SET last_login = NOW() WHERE email='$email'"); 
       // user authentication details are correct 
       return $result; 
      } 
     } else { 
      // user not found 
      return false; 
     } 
    }